MXPTiny software can capture any bit rate in H.264 but only with BMD H.264 Pro Recorder or TVS. https://ianmorrish.wordpress.com/2016/08/25/record-h-264-from-blackmagic-television-studio-usb-port/
I suspect because of the raw data rate of the DeckLink API you would need a lot of processing power to encode with compression to meet the bit rate you want to select.
This is good for archiving or streaming content but no linear editing which the codecs you mention are designed for and is why they have fixed bit rates.
TGA files may be saved compressed (run length encoded) or not compressed.
To work in the media pool they must be uncompressed which is not the default when exporting from many graphics apps.